Re: Question about CONVERT(str,charset_to,charset_from)

[Michael Widenius]

Hi!

>>>>> "Alexander" == Alexander Barkov <Alexander> writes:

Alexander> Paul DuBois wrote:
>> I've been puzzling over this patch, which implements a form of the
>> CONVERT() function.  I can see that this can be useful for specifying
>> the destination character set as a string expression rather than as
>> an unquoted character set name.  But I'm wondering why the second argument
>> is necessary at all.  Strings have a charset already, why do you have
>> to specify what it is?



bar> There are some reasons against this style of CONVERT():

bar>    CONVERT(string,from_charset,to_charset)

I thought you implemented this function.

bar> They are:

bar> 1. As we lately decided, a function should never return strings
bar>     with different charsets in different rows. The above style of
bar>     CONVERT() breaks this rule.

<cut>

bar> So, taking all this in account, I can suppose:

bar> 1. we should remove this style: CONVERT(expr,expr,expr), as far
bar>     as it can produce strings in different charsets in
bar>     different rows, which is wrong;

bar> 2. we can't extend COLLATE to support expression:
bar>     SELECT body COLLATE expr
bar>     because it will be able to produce different charsets
bar>     in different rows again.

bar> Probably, the case is to extend CONVERT syntax to support
bar> something like this:

bar> CONVERT(expr FROM expr USING unquoted_charset_name)

bar>   where the first expr is a source string to convert and the
bar>   second expr is a source charset. This will not reduce a
bar>   functionality and also will not break the rule about
bar>   different charsets in rows.

bar> What do you think?

Yes, the above would be ok.

Regards,
Monty
CTO of MySQL AB